This invention relates to a novel method for selectively etching an integral or unitary cathode substrate and support; and particularly, although not exclusively, to selectively etching a cylindrical one-piece bimetal cathode substrate and support sleeve.
A one-piece bimetal cathode substrate and support sleeve is disclosed in RCA Technical Notes TN No. 1159 mailed July 23, 1976. That one-piece part is described generally as a cup-shaped nickel-alloy cathode substrate integrally supported on a thin cylinder and endwall of a structural alloy such as a nickel-chromium alloy. The part is fabricated from a bimetal laminate comprised of layers of the two alloys which are clad or otherwise joined together. That one-piece part has been fabricated by the general method disclosed in U.S. Pat. No. 3,432,900 issued March 18, 1969 to D. R. Kerstetter. By this method, a cup-and-sleeve is deep drawn from a bimetal laminate strip. Then, selected portions of the nickel-alloy layer are removed by etching. The etching is achieved by selectively masking the surface of the nickel-alloy layer with an etch-resistant material and then etching away the unmasked portions with a liquid etchant. The etch-resistant material is applied by painting or spraying or by some photographic technique and then later removed. This prior method is generally labor intensive and costly.